In the field of medical image technology, Positron Emission Tomography (PET) or gamma cameras are often combined with Computed Tomography (CT) systems. To conduct a so-called PET scan, a short-lived radioactive tracer isotope, which decays by emitting a positron, is injected usually into the blood circulation of a living subject. After the metabolically active molecule becomes concentrated in tissues of interest, the research subject or patient is placed in the imaging scanner. The molecule most commonly used for this purpose is fluorodeoxyglucose (FDG), a sugar, for which the waiting period is typically an hour.
As the radioisotope undergoes positron emission decay, it emits a positron, the antimatter counterpart of an electron. After traveling up to a few millimeters the positron encounters and annihilates with an electron, producing a pair of gamma photons moving in almost opposite directions. These are detected when they reach one of a plurality of scintillator crystals in the scanning device, creating a burst of light which is detected by photomultiplier tubes (PMT) or silicon avalanche photodiodes (Si APD). The technique depends on simultaneous or coincident detection of the pair of photons along respective lines of response (LOR). Due to the nature of the system, a relative complex normalization, time alignment and quality check needs to be performed on the PET scanner part. Moreover, as the CT and PET scanners are very different systems, and produces different kind of images, the system needs to be calibrated with respect to the PET/CT gantry offset. A variety of different calibration methods for each system is known.
Conventional PET/CT devices use specific phantoms to perform the PET/CT gantry offset task, another phantom source to perform the PET setup task, and yet another phantom source to perform the PET time alignment, normalization, and quality check tasks. These tasks need to be performed very often, sometimes daily, especially for mobile PET/CT systems, to maintain a good image quality.
In order to perform the tasks mentioned above, each time a technician or a service personal has to put a different phantom on and off the scanner. This process is time consuming. Moreover, technicians are unnecessarily exposed to the radiation dose of the different phantoms. Also, handling these phantoms can be difficult as some of these phantoms weight around 10 lb or more.
Hence, there exists a need for an apparatus and method for performing PET/CT gantry offset, PET setup, time alignment, normalization, and quality check with a single device. In addition there is a need for an automated procedure to perform such calibrations.